Chapter 12 - Nervous Tissue Flashcards Preview

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Flashcards in Chapter 12 - Nervous Tissue Deck (45):
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Nervous system is responsible for all our __, ___ and __. 

behaviors

memories 

movements

2

neurology

branch of medical science that deals with normal functioning & disorders of the NS

3

Major structures of the NS 

12 pairs of cranial nerves

31 pairs of spinal nerves 

ganglia outside CNS - small masses of nervous tissue, mostly neuronal cell bodies

Enteric plexuses - help regulate digestive system - neuron networks in walls of GI tract organs 

sensory receptors - structure of NS that monitors change in internal/external environment 

4

Functions of NS (3) 

1) sensory - afferent 

2) integrative - interneurons

3) motor - efferent

5

NS divisions (2) 

CNS  - brain & spinal cord

PNS - cranial & spinal nerves, connects CNS to muscles/glands/sensory receptors

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Neurons

functional unit of nervous system

have capacity to produce action potentials - electrical excitability 

cell body (soma) - contains organelles

Nissl bodies - clusters of rough ER

neurofibrils - cell shape & support

microtubules - assist in moving materials 

dendrites & axons - processes

lipofuscin - yellow/brown pigment granules in cytoplasm

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Location for most protein synthesis in Neuron

cell body

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Axonal transport 

1) slow axonal flow

2) fast axonal flow

1) movement in one direction  -away from cell body

2) either direction - use or recycling 

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Structural classification of neurons

1) multipolar

2) bipolar

3) unipolar

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Functional classification of Neurons

1) sensory (afferent) 

2) motor (efferent) 

3) interneurons (association) 

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Neuroglia 

non-neuronal cells

1/2 the volume of CNS 

Of CNS: astrocytes, oligodendrocytes, microglia, ependymal

Of PNS: Schwann, satellite

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Neuroglia of CNS 

1) astrocytes

2) oligodendrocytes

3) microglia

4) ependymal 

1) support, blood-brain barrier, homeostasis, 

2) form myelin sheath around axons

3) phagocytes

4) produce cerebrospinal fluid 

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Neuroglia of PNS

1) schwann cells

2) satellite 

1) form myelin sheath around ONE axon 

2) structural support & regulate exchange of materials b/w soma & interstitial fluid

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Schwann cell cytoplasm forms outer layer & inner layer is...

myelin sheath (100+ layers of schwann cell membrane) 

15

Subdivisions of PNS 

1) Somatic (voluntary) - cutaneous &special sensory receptors → CNS 

motor neurons → skeletal muscle

2) Autonomic (involuntary) - sensory- visceral organs → CNS

motor to smooth+cardiac muscle& glands

A. Sympathetic - ↑ heart rate

B. Parasympathetic - ↓ heart rate

3) Enteric - involuntary sensory & motor control GI tract 

function independently of ANS & CNS 

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Neurons are electrically excitable due to  the?

voltage difference across their membrane

17

Neurons communicate with (2) types of electric signals

1) action potentials - long distance 

2) graded potentials - short distance

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Resting membrane potential

What is potential energy difference at rest?

When neuron is at rest,

negative ions along inside of cell membrane & positive ions along outside 

 

-70mV

 

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At rest, Neuron is said to be _____

polarized

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Resting potential exists because? (3) 

1) ion concentration differs from inside to outside

ECF has lots of Na+ & Cl-

cytosol has lots of K+

2) inability of most anions to leave cell - membrane permeability differs for Na+ & K+

3) Electrogenic nature of Na+/K+  ATPase

- inward flow of Na+ cant keep up with outward flow of K+ ( Na+ pumped out as fast as it leaks in) 

this removes more positive than it brings in 

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Graded potential

occur mainly in?

dendrites & neuronal cell bodies 

small deviation from resting potential of -70mV

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hyperpolarizing vs depolarizing 

hyperpolarizing - membrane becomes more negative

depolarizing - membrane become more positive

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Graded potential

The signals are graded, meaning they vary in... and are? (2) 

 

1) amplitude (size), 
depending on the strength of the stimulus 

2) localized 

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Action Potential (impulse) 

a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and then restore it to resting state (repolarization

25

All-or-none principle of Action Potentials

if stimulus reaches threshold, the action potential produced is always the same

stronger stimulus does NOT produce large impulse

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(3) phases of an action potential

1) depolarizing phase

2) repolarizing phase

3) hyperpolarizing phase

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1) depolarizing phase

 

At rest: inactivation Na+ gate = open, activation gate = closed

chemical/mechanical stimulus → graded potential reaches threshold (-55mV) → Na+ channels open → inactivation gate closes  → membrane potential = +30mV 

 

 

 

 

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2) repolarizing phase

 

 

when threshold potential reached (-55mV) → K+ channels open (much slower than Na+ channels) → once K+ channels are open, Na+ channels are closed again → K+ outflow returns membrane potential to -70mV

 

 

 

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3) hyperpolarizing phase
 

if enough K+ leaves cell, membrane potential reaches -90mV 

K+ channels close & membrane potential returns to resting potential (-70mV) 

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Refractory period

 

Period of time during which neuron can not generate another action potential

31

Absolute refractory period vs Relative refractory period

absolute - (depolarzing + repolarizing phase) 

even very strong stimulus can not begin another AP

inactivated Na+ channels must return to resting state 

 

refractory - (hyperpolarizing phase) 

 A suprathreshold stimulus will be able to start AP 

K+ channels still open but Na+ channels are closed 

32

Conduction - (2) types

1) continuous 

2) saltatory

1) unmyelinated + muscle fibers - step-by-step depolarization of each portion of the length of the axolemma (axon plasma membrane) 

2) myelinated axons - depolarization only at nodes of Ranvier (gaps in myelin sheath) where there is a high density of voltage-gated ion channels

current carried by ions flows through ECF from node to node

 

33

Factors that affect speed of propagation (3) 

1) amount of myelination - faster along myelinated axon

2) axon diameter - larger = faster

3) temperature - higher temp = faster

34

The propagation speed of a nerve impulse is not related to __ __

 

stimulus strength. 

35

Fiber types (3) 

diameterm, absolute refractory period (ARP), myelinated/unmyelinated, sensory/motor

A fibers - largest, longest ARP

- myelinated somatic sensory & motor to skeletal muscle

B fibers - medium, faster ARP

- myelinated visceral sensory & autonomic preganglionic (CNS → ANS relay station)

C fibers - smallest, fastest ARP 

unmyelinated sensory & autonomic motor 

36

(2) types of synapses 

1) electrical 

2) chemical

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Electrical Synapse

 ionic current spreads to next cell through gap junctions

faster, two-way transmission & capable of synchronizing groups of neurons

AP conduct directly between plasma membrane of adjacent neuron through gap junctions) 

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Chemical synapse

one-way information transfer from presynaptic to postsynaptic neuron

plasma membranes do not touch, seperated by synaptic cleft 

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1) axodendritic 
2) axosomatic 

3) axoaxonic 

 

1) from axon to dendrite 

2) from axon to cell body 

3) from axon to axon 

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Signal transmission at chemical synapse

Action potential reaches end bulb and voltage-gated Ca2+ channels open → Ca2+ inward flow triggers release of neurotransmitters → cross synaptic cleft & bind to ligand-gated receptors → channels open on postsynaptic neuron & ions flow across 

 

41

Both ____________ and ____________ neurotransmitters are present in the CNS and PNS

the same ____________ may be excitatory in some 
locations and inhibitory in others. 

 

inhibitory & excitatory 

neurotransmitter

42

Important neurotransmitters include? (8) 

 acetylcholine, glutamate, aspartate, gamma aminobutyric acid, glycine, norepinephrine, epinephrine, and 

dopamine. 

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Neural circuits

involved in many important activities such as? (3) 

functional groups of neurons that process specific types of information 

breathing, short-term memory. waking up

44

Types of neural circuits (5) 

1) simple series 

2) diverging

3) converging

4) reverberating

5) parallel after-discharge 

 

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